FIG. 1 illustrates a system for determining three-dimensional coordinates using the principle of a laser interferometer. The principle is that laser beams generated from an x-axis laser interferometer 1a, a y-axis laser interferometer 1b and a z-axis laser interferometer 1c are inputted into a probe 3a and interference patterns reflected by corner mirrors 2a, 2b and 2c of the probe are detected to set the three-dimensional coordinates. In this system, the operating range of the probe 3a increases when the volume of an object to be measured is large. In the above-described procedure, the laser interferometers 1a, 1b and 1c are failed to target the ranges of the corner mirrors of the probe so that the coordinate values cannot be measured. In addition, the laser interferometers must move together with the probe as the probe moves and they are costly apparatuses. Thus, a three-dimensional measurer employing the principle of the laser interferometer becomes expensive.
To overcome the aforementioned shortcoming, another system using a laser interferometer (shown in FIG. 1A) is constructed in a manner that x-axis and y-axis reflecting mirrors 2x and 2y reflect interference patterns and z-axis measures a laser interferometer apparatus using the laser interferometer. However, this system should use two laser interferometers and employ reflecting mirrors 2x and 2y, which are perfectly horizontal. Accordingly, the system becomes expensive and the sizes of the reflecting mirrors must be increased when the movement range of the probe is extended.
FIGS. 2 and 2A illustrate laser interferometers that compensate for the shortcomings of the systems of FIGS. 1 and 1A. Laser interferometers 1e, 1f, 1g and 1h are located irrespective of directions and an interference pattern reflected by a corner mirror 2d set at one side of a probe is detected to measure three-dimensional coordinates. This system includes a controller 91 for setting a position of the probe and a computer 90 for detecting the interference pattern to measure the three-dimensional coordinates. This system is also expensive because it uses four laser interferometers. In addition, the laser interferometers should rotate when the probe is moved.